Chemotherapy (also called chemo) is a type of cancer treatment that uses drugs to destroy cancer cells. It works by stopping or slowing the growth of cancer cells, which grow and divide quickly.
But it can also harm healthy cells that divide quickly, such as those that line your mouth and intestines or cause your hair to grow. Damage to healthy cells may cause side effects. Often, side effects get better or go away after chemotherapy is over.
Depending on the type of cancer and how advanced it is, chemotherapy can:
- Cure cancer – when chemotherapy destroys cancer cells to the point that the doctor can no longer detect them in your body and they will not grow back.
- Control cancer – when chemotherapy keeps cancer from spreading, slows its growth, or destroys cancer cells that have spread to other parts of the body.
- Ease cancer symptoms (also called palliative care) – when chemotherapy shrinks tumors that are causing pain or pressure.
Radiation therapy (also called radiotherapy, x-ray therapy, or irradiation) is the use of a certain type of energy (called ionizing radiation) to kill cancer cells and shrink tumors. Radiation therapy injures or destroys cells in the area being treated (the “target tissue”) by damaging their genetic material, making it impossible for these cells to continue to grow and divide. Although radiation damages both cancer cells and normal cells, most normal cells can recover from the effects of radiation and function properly. The goal of radiation therapy is to damage as many cancer cells as possible, while limiting harm to nearby healthy tissue.
There are different types of radiation and different ways to deliver the radiation. For example, certain types of radiation can penetrate more deeply into the body than can others. In addition, some types of radiation can be very finely controlled to treat only a small area (an inch of tissue, for example) without damaging nearby tissues and organs. Other types of radiation are better for treating larger areas.
In some cases, the goal of radiation treatment is the complete destruction of an entire tumor. In other cases, the aim is to shrink a tumor and relieve symptoms. In either case, doctors plan treatment to spare as much healthy tissue as possible.
About half of all cancer patients receive some type of radiation therapy. Radiation therapy may be used alone or in combination with other cancer treatments, such as chemotherapy or surgery. In some cases, a patient may receive more than one type of radiation therapy.
Surgery is an operation to remove cancer. The side effects of surgery depend on many factors, including the size and location of the tumor, the type of operation, and the patient’s general health. Patients have some pain after surgery, but this pain can be controlled with medicine. It is also common for patients to feel tired or weak for a while after surgery.
Patients may worry that having a biopsy or other type of surgery for cancer will spread the disease. This is a very rare occurrence because surgeons take special precautions to prevent cancer from spreading during surgery. Also, exposing cancer to air during surgery does not cause the disease to spread.
Hormone therapy is used to treat certain cancers that depend on hormones for their growth. It works by keeping cancer cells from getting or using the hormones they need to grow. This treatment may include the use of drugs that stop the production of certain hormones or that change the way hormones work. Another type of hormone therapy is surgery to remove organs that make hormones. For example, the ovaries may be removed to treat breast cancer, or the testicles may be removed to treat prostate cancer.
Hormone therapy can cause a number of side effects. Patients may feel tired, or have fluid retention, weight gain, hot flashes, nausea and vomiting, changes in appetite, and, in some cases, blood clots. Hormone therapy may also cause bone loss in premenopausal women. Depending on the type of hormone therapy used, these side effects may be temporary, long lasting, or permanent.
Biological therapy is a type of treatment that works with the immune system. It can help fight cancer or help control side effects from other cancer treatments like chemotherapy.
Biological therapy and chemotherapy are both treatments that fight cancer. While they may seem alike, they work in different ways. Biological therapy helps your immune system fight cancer, whereas chemotherapy attacks the cancer cells directly.
Doctors are not sure how biological therapy helps the immune system fight cancer. But they think it may:
- Stop or slow the growth of cancer cells.
- Make it easier for the immune system to destroy, or get rid of, cancer cells.
- Keep cancer from spreading to other parts of the body
Angiogenesis is the formation of new blood vessels. Angiogenesis is a process controlled by certain chemicals produced in the body. Some of these chemicals stimulate cells to repair damaged blood vessels or form new ones. Other chemicals, called angiogenesis inhibitors, signal the process to stop.
Angiogenesis plays an important role in the growth and spread of cancer. New blood vessels “feed” the cancer cells with oxygen and nutrients, allowing these cells to grow, invade nearby tissue, spread to other parts of the body, and form new colonies of cancer cells.
Because tumors cannot grow or spread without the formation of new blood vessels, scientists are trying to find ways to stop angiogenesis. They are studying natural and synthetic angiogenesis inhibitors, also called antiangiogenic agents, in the hope that these chemicals will prevent or slow down the growth of cancer by blocking the formation of new blood vessels.
Bone Marrow Transplantation and Peripheral Blood Stem Cell Transplantation
Bone marrow transplantation (BMT) and peripheral blood stem cell transplantation (PBSCT) are procedures that restore stem cells that have been destroyed by high doses of chemotherapy and/or radiation therapy.
There are three types of transplants:
- In autologous transplants, patients receive their own stem cells.
- In syngeneic transplants, patients receive stem cells from their identical twin.
- In allogeneic transplants, patients receive stem cells from their brother, sister, or parent. A person who is not related to the patient (an unrelated donor) also may be used.
One reason BMT and PBSCT are used in cancer treatment is to make it possible for patients to receive very high doses of chemotherapy and/or radiation therapy. To understand more about why BMT and PBSCT are used, it is helpful to understand how chemotherapy and radiation therapy work.
Chemotherapy and radiation therapy generally affect cells that divide rapidly. They are used to treat cancer because cancer cells divide more often than most healthy cells. However, because bone marrow cells also divide frequently, high-dose treatments can severely damage or destroy the patient’s bone marrow. Without healthy bone marrow, the patient is no longer able to make the blood cells needed to carry oxygen, fight infection, and prevent bleeding. BMT and PBSCT replace stem cells that were destroyed by treatment. The healthy, transplanted stem cells can restore the bone marrow’s ability to produce the blood cells the patient needs.
In some types of leukemia, the graft-versus-tumor (GVT) effect that occurs after allogeneic BMT and PBSCT is crucial to the effectiveness of the treatment. GVT occurs when white blood cells from the donor (the graft) identify the cancer cells that remain in the patient’s body after the chemotherapy and/or radiation therapy (the tumor) as foreign and attack them.
BMT and PBSCT are most commonly used in the treatment of leukemia and lymphoma. They are most effective when the leukemia or lymphoma is in remission (the signs and symptoms of cancer have disappeared). BMT and PBSCT are also used to treat other cancers such as neuroblastoma (cancer that arises in immature nerve cells and affects mostly infants and children) and multiple myeloma. Researchers are evaluating BMT and PBSCT in clinical trials for the treatment of various types of cancer.
Cryosurgery (also called cryotherapy) is the use of extreme cold produced by liquid nitrogen (or argon gas) to destroy abnormal tissue. Cryosurgery is used to treat external tumors, such as those on the skin. For external tumors, liquid nitrogen is applied directly to the cancer cells with a cotton swab or spraying device.Cryosurgery is also used to treat tumors inside the body (internal tumors and tumors in the bone). For internal tumors, liquid nitrogen or argon gas is circulated through a hollow instrument called a cryoprobe, which is placed in contact with the tumor. The doctor uses ultrasound or MRI to guide the cryoprobe and monitor the freezing of the cells, thus limiting damage to nearby healthy tissue. (In ultrasound, sound waves are bounced off organs and other tissues to create a picture called a sonogram.) A ball of ice crystals forms around the probe, freezing nearby cells. Sometimes more than one probe is used to deliver the liquid nitrogen to various parts of the tumor. The probes may be put into the tumor during surgery or through the skin (percutaneously).
After cryosurgery, the frozen tissue thaws and is either naturally absorbed by the body (for internal tumors), or it dissolves and forms a scab (for external tumors).
Advances in understanding and manipulating genes have set the stage for scientists to alter a person’s genetic material to fight or prevent disease. Gene therapy is an experimental treatment that involves introducing genetic material (DNA or RNA) into a person’s cells to fight disease. Gene therapy is being studied in clinical trials for many different types of cancer and for other diseases. It is not currently available outside a clinical trial.
Researchers are studying several ways to treat cancer using gene therapy. Some approaches target healthy cells to enhance their ability to fight cancer. Other approaches target cancer cells, to destroy them or prevent their growth. Some gene therapy techniques under study are described below.
In one approach, researchers replace missing or altered genes with healthy genes. Because some missing or altered may cause cancer, substituting “working” copies of these genes may be used to treat cancer.
Researchers are also studying ways to improve a patient’s immune response to cancer. In this approach, gene therapy is used to stimulate the body’s natural ability to attack cancer cells. In one method under investigation, researchers take a small blood sample from a patient and insert genes that will cause each cell to produce a protein called a T-cell receptor (TCR). The genes are transferred into the patient’s white blood cells (called T lymphocytes) and are then given back to the patient. In the body, the white blood cells produce TCRs, which attach to the outer surface of the white blood cells. The TCRs then recognize and attach to certain molecules found on the surface of the tumor cells. Finally, the TCRs activate the white blood cells to attack and kill the tumor cells.
Scientists are investigating the insertion of genes into cancer cells to make them more sensitive to chemotherapy, radiation therapy, or other treatments. In other studies, researchers remove healthy blood-forming stem cells from the body, insert a gene that makes these cells more resistant to the side effects of high doses of anticancer drugs, and then inject the cells back into the patient.
In another approach, researchers introduce “suicide genes” into a patient’s cancer cells. A pro-drug (an inactive form of a toxic drug) is then given to the patient. The pro-drug is activated in cancer cells containing these “suicide genes,” which leads to the destruction of those cancer cells.
Other research is focused on the use of gene therapy to prevent cancer cells from developing new blood vessels (angiogenesis).
Hyperthermia (also called thermal therapy or thermotherapy) is a type of cancer treatment in which body tissue is exposed to high temperatures (up to 113°F). Research has shown that high temperatures can damage and kill cancer cells, usually with minimal injury to normal tissues (1). By killing cancer cells and damaging proteins and structures within cells (2), hyperthermia may shrink tumors.
Hyperthermia is under study in clinical trials (research studies with people) and is not widely available. It is almost always used with other forms of cancer therapy, such as radiation therapy and chemotherapy. Hyperthermia may make some cancer cells more sensitive to radiation or harm other cancer cells that radiation cannot damage. When hyperthermia and radiation therapy are combined, they are often given within an hour of each other. Hyperthermia can also enhance the effects of certain anticancer drugs.
Laser therapy uses high-intensity light to treat cancer and other illnesses. Lasers can be used to shrink or destroy tumors. Lasers are most commonly used to treat superficial cancers (cancers on the surface of the body or the lining of internal organs) such as basal cell skin cancer and the very early stages of some cancers, such as cervical, penile, vaginal, vulvar, and non-small cell lung cancer.
Lasers also may be used to relieve certain symptoms of cancer, such as bleeding or obstruction. For example, lasers can be used to shrink or destroy a tumor that is blocking a patient’s trachea (windpipe) or esophagus. Lasers also can be used to remove colon polyps or tumors that are blocking the colon or stomach.
Laser therapy can be used alone, but most often it is combined with other treatments, such as surgery, chemotherapy, or radiation therapy. In addition, lasers can seal nerve endings to reduce pain after surgery and seal lymph vessels to reduce swelling and limit the spread of tumor cells.
Laser therapy is often given through a flexible endoscope (a thin, lighted tube used to look at tissues inside the body). The endoscope is fitted with optical fibers (thin fibers that transmit light). It is inserted through an opening in the body, such as the mouth, nose, anus, or vagina. Laser light is then precisely aimed to cut or destroy a tumor.
Laser-induced interstitial thermotherapy (LITT) (or interstitial laser photocoagulation) also uses lasers to treat some cancers. LITT is similar to a cancer treatment called hyperthermia, which uses heat to shrink tumors by damaging or killing cancer cells
During LITT, an optical fiber is inserted into a tumor. Laser light at the tip of the fiber raises the temperature of the tumor cells and damages or destroys them. LITT is sometimes used to shrink tumors in the liver.
Photodynamic therapy (PDT) is another type of cancer treatment that uses lasers. In PDT, a certain drug, called a photosensitizer or photosensitizing agent, is injected into a patient and absorbed by cells all over the patient’s body. After a couple of days, the agent is found mostly in cancer cells. Laser light is then used to activate the agent and destroy cancer cells. Because the photosensitizer makes the skin and eyes sensitive to light for approximately 6 weeks, patients are advised to avoid direct sunlight and bright indoor light during that time.
In the first step of PDT for cancer treatment, a photosensitizing agent is injected into the bloodstream. The agent is absorbed by cells all over the body, but stays in cancer cells longer than it does in normal cells. Approximately 24 to 72 hours after injection, when most of the agent has left normal cells but remains in cancer cells, the tumor is exposed to light. The photosensitizer in the tumor absorbs the light and produces an active form of oxygen that destroys nearby cancer cells.
In addition to directly killing cancer cells, PDT appears to shrink or destroy tumors in two other ways. The photosensitizer can damage blood vessels in the tumor, thereby preventing the cancer from receiving necessary nutrients. In addition, PDT may activate the immune system to attack the tumor cells.
The light used for PDT can come from a laser or other sources of light. Laser light can be directed through fiber optic cables (thin fibers that transmit light) to deliver light to areas inside the body. For example, a fiber optic cable can be inserted through an endoscope (a thin, lighted tube used to look at tissues inside the body) into the lungs or esophagus to treat cancer in these organs. Other light sources include light-emitting diodes (LEDs), which may be used for surface tumors, such as skin cancer.
PDT is usually performed as an outpatient procedure. PDT may also be repeated and may be used with other therapies, such as surgery, radiation, or chemotherapy.
Targeted Cancer Therapies
Targeted cancer therapies use drugs that block the growth and spread of cancer. They interfere with specific molecules involved in carcinogenesis (the process by which normal cells become cancer cells) and tumor growth. Because scientists call these molecules “molecular targets,” these therapies are sometimes called “molecular-targeted drugs,” “molecularly targeted therapies,” or other similar names. By focusing on molecular and cellular changes that are specific to cancer, targeted cancer therapies may be more effective than current treatments and less harmful to normal cells.
Most targeted cancer therapies are in preclinical testing (research with animals), but some are in clinical trials (research studies) or have been approved by the U.S. Food and Drug Administration (FDA). Targeted cancer therapies are being studied for use alone, in combination with each other, and in combination with other cancer treatments, such as chemotherapy.
For a detailed explanation on all the types of cancer treatments, please visit www.cancer.gov.
Source: National Institute of Cancer
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